I think that Pete Hines did say something aboyt this in an interview somewhere with someone (sorry I can't remember where, but it could be on gamasutra)
Pete Hines said about a MMORPG that it needed to be a fresh approach, possibly meaning a fresh IP, not an old one like TES. So, no, I don't think that there will be
a MMO set in Tamriel, nor on Nirn.
TES 5, will for me, anyway, be about the powerstruggle on who is going to have the power in Tamriel, Chancellor Ocato, the Elder Council or the Nobles (or maybe the people?). The main quest could feature more (mature) political content where your protagonist had to choose which imperial factions he would support, and then there could be certain sidequests fleshed out from the main quest so that the game
more than Oblivion would feel like a unified whole game, meaning that the sidequests and main quests sort of grab and grib and intertwine between each other.
This would be great
However, I fear and I'm concerned about Bethesda Softworks already have chosen their (console) future, catering to what they think is the (action) console crowd.
So my best guess is that Bethesda will widen & develop the radiant AI more, the game will start featuring small fire arms, such as the fint pistols of the 17th century, and the game's combat will be more like FPS combat with no depending on stats and abilities, just the trigger finger of the player. To me, that would be sad
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but apparently that is what sells these days